1. Technical Field of the Invention
This invention relates to insulating rolls and has particular reference to an improved type of insulating roll which has low thermal conductivity and high impact strength without involving reduced surface temperature of materials being heat treated in a furnace (of materials being rolled), or reduced ambient temperature in the furnace during heat treatment.
2. Description of the Related Art
Certain rolls are generally known as insulating rolls, and they include a transport roll used in a process step of heat treatment wherein stainless steel tubes are welded with each other, a sealing roll used in a preheating step of steel in a reducing furnace so as to shield the ambient furnace gas at the inlet and outlet of the furnace, and a transport roll used in transporting a material to be treated in a furnace.
Those known insulating rolls have been so structured as to follow either one of two sorts of conventional practice disclosed in Japanese Unexamined Patent Publication No. 9-125157. First such practice is directed, as shown in FIGS. 1 and 2 of the accompanying drawings, to a roll constructed with a metal conduit 1 and an outer tube 7 made of thermally resistant metal. The outer tube 7 is firmly attached to the metal conduit 1 by flanges 3, 4 located at opposite ends of the outer tube 7 and by one or more metallic support rings 40 fixed peripherally between the flanges 3, 4. To provide water cooling, the metal conduit 1 allows passage of cooling water therethrough. The last practice is seen in FIG. 3 wherein a thermal insulating material 50, as of a fibrous ceramic is filled in a space defined between the metal conduit 1 and the outer tube 7 of thermally resistant metal. However, the conventional insulating rolls noted here have experienced the problems set forth below.
Firstly, the first practice of the prior publication cited above produces an insulating roll having all of its constituent members made of metal. This means that the roll invites too high a thermal conductivity and hence cools the outer tube as well, reducing the temperature of the material being treated and the ambient temperature in the furnace. The temperature drop is found particularly sharp at a region in proximity to the support flange fixed peripherally of the metal conduit in attaining firm attachment of the outer tube.
To make a spacious flange-to-flange arrangement for avoiding the temperature drop, the outer tube is required to have a large thickness. Furthermore, the roll produced by the first practice is problematic in its working atmosphere as it is extremely noisy due to shock caused upon contact of the roll with a material to be transported.
Next, the last practice leads to an insulating roll in which a pad of thermal insulating fiber or mortar has been packed in a space defined between the metal conduit and the outer tube. This pad is used to gain improved thermal insulation of the roll and stabilized support of the outer tube with respect to the metal conduit, or to otherwise obviate the drawbacks encountered in the first practice. However, the insulating fiber or insulating mortar becomes deteriorated and powdery upon exposure to repeated rise and fall of the furnace temperature. The result is the failure to adequately support the outer tube, which brings about a deformed or warped roll. Additionally, it is difficult to pack a bulky fibrous pad uniformly during production of the roll, and this is responsible for irregular packing density with consequent warping of the roll. Though easy to pack, mortar is apt to get dry and hence shrink over an extended period of time after packing, thereby creating gaps in the pad.